1. Field of the Invention
The present invention generally relates to apparatus for balancing out-of-balance rotary bodies and more particularly concerns an apparatus for measuring the magnitude and angular position of imbalance in at least one plane of a rotary body such as a motor vehicle wheel.
2. Description of the Prior Art
In the dynamic balancing of a rotary body such as a motor vehicle wheel, the wheel is rotated on the vehicle with measurements made directly thereto, or the wheel is removed from the vehicle and mounted on a special drive shaft and then rotated. When the drive shaft and wheel are spun, the out-of-balance forces cause the drive shaft to move slightly off-axis in a measuring plane, and force transducers in the measuring plane provide signals which are proportional to the magnitude of the unbalanced forces. The location of the unbalanced weight is then determined, by means of the transducers, with respect to the planes through the inner and outer rims of the wheel. To then bring the wheel into dynamic and static balance the operator applies weight to the inner and outer rims of the wheel at the unbalanced weight locations as determined by the transducers until the drive shaft remains on-axis as the wheel is rotated.
In U.S. Pat. No. 3,835,712 to Muller, an apparatus for dynamically balancing a rotary body is disclosed wherein the wheel to be balanced is rotated on a balancing shaft. A phase displacement device (i.e., a synchro or a resolver) is also provided on the shaft. The shaft is rotated to spin the wheel at its normal rotational speed, and a force transducer produces a force signal which is indicative of the magnitude of the unbalanced wheel weight. The location of the unbalanced weight is provided in an output signal by using the force signal to phase shift a reference voltage by an angular amount indicative of the position of the unbalanced weight. As the wheel is subsequently slowed to a stop, the reference voltage is applied to the stator windings of the phase displacement device so that the rotor thereof will provide an output signal comprising the reference voltage phase shifted by an amount indicative of the position of the wheel. When the wheel stops, the two phase shifted signals are compared by means including a null meter, and the wheel is rotated until a null is obtained at which time the unbalanced weight position will be in a predetermined rotative position of the wheel so that the balancing weight can be accurately and easily added to the wheel. While the balancing apparatus of the Muller patent operates in an entirely satisfactory and accurate manner, it will be recognized that it is comprised of complex and expensive components which significantly add to the cost of the apparatus.
In U.S. Pat. No. 3,910,121 to Curchod et al, a two-plane dynamic wheel balancing machine is disclosed which includes a force transmission member which is supported for movement in one plane. The drive shaft of the balancer is mounted on the force transmission member such that the imbalance forces tend to move the member in the plane in which it is mounted, and force transducers produce signals indicative of the position and magnitude of the imbalance forces in the two planes of the wheel to be balanced. A photoelectric device produces a reference signal when the shaft rotates through a predetermined reference position, and another photoelectric device produces position pulse signals indicative of the angular position of the shaft with respect to said reference signal. The position pulses are counted, and the counter is read when the unbalanced weight is in a predetermined rotative position of the wheel. When the wheel stops, the operator rotates the wheel until the counter reading is again at the number which indicates said predetermined rotative wheel position where the balancing weights are applied.
U.S. Pat. No. 3,732,737 to Forster discloses a two-plane dynamic wheel balancing apparatus which operates in a manner similar to that of the aforedescribed Curchod et al device in that the positions at which the counterbalance weights are to be attached to the wheel rims are determined by measuring the phases of analog signals from the force transducers relative to some fixed reference point on the balancing shaft.